stopping polluting the earthhope to live in a better environment．A. Only to；we CallB. Only

问题补充：

stopping polluting the earthhope to live in a better environment．

A. Only to；we Call

B. Only to；can we

C. Only by；can we

D. Only by；we can

答案：

A. Only to；we Call

B. Only to；can we

(答案→)C. Only by；can we

D. Only by；we can

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